LXR linux/Documentation/networking/mac80211-injection.txt

   1How to use packet injection with mac80211
   2=========================================
   3
   4mac80211 now allows arbitrary packets to be injected down any Monitor Mode
   5interface from userland.  The packet you inject needs to be composed in the
   6following format:
   7
   8 [ radiotap header  ]
   9 [ ieee80211 header ]
  10 [ payload ]
  11
  12The radiotap format is discussed in
  13./Documentation/networking/radiotap-headers.txt.
  14
  15Despite many radiotap parameters being currently defined, most only make sense
  16to appear on received packets.  The following information is parsed from the
  17radiotap headers and used to control injection:
  18
  19 * IEEE80211_RADIOTAP_FLAGS
  20
  21   IEEE80211_RADIOTAP_F_FCS: FCS will be removed and recalculated
  22   IEEE80211_RADIOTAP_F_WEP: frame will be encrypted if key available
  23   IEEE80211_RADIOTAP_F_FRAG: frame will be fragmented if longer than the
  24                              current fragmentation threshold.
  25
  26
  27The injection code can also skip all other currently defined radiotap fields
  28facilitating replay of captured radiotap headers directly.
  29
  30Here is an example valid radiotap header defining some parameters
  31
  32        0x00, 0x00, // <-- radiotap version
  33        0x0b, 0x00, // <- radiotap header length
  34        0x04, 0x0c, 0x00, 0x00, // <-- bitmap
  35        0x6c, // <-- rate
  36        0x0c, //<-- tx power
  37        0x01 //<-- antenna
  38
  39The ieee80211 header follows immediately afterwards, looking for example like
  40this:
  41
  42        0x08, 0x01, 0x00, 0x00,
  43        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
  44        0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
  45        0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
  46        0x10, 0x86
  47
  48Then lastly there is the payload.
  49
  50After composing the packet contents, it is sent by send()-ing it to a logical
  51mac80211 interface that is in Monitor mode.  Libpcap can also be used,
  52(which is easier than doing the work to bind the socket to the right
  53interface), along the following lines:
  54
  55        ppcap = pcap_open_live(szInterfaceName, 800, 1, 20, szErrbuf);
  56...
  57        r = pcap_inject(ppcap, u8aSendBuffer, nLength);
  58
  59You can also find a link to a complete inject application here:
  60
  61http://wireless.kernel.org/en/users/Documentation/packetspammer
  62
  63Andy Green <andy@warmcat.com>
  64